The infinitive is the most versatile verb form because it can be used as a verb, noun, adjective and even an adverb. An infinitive verb is a non-finite verb; it cannot be used as the main verb in a sentence. The infinitive verb form is usually preceded by the word "to". For example: to run, to dance, to swim, to sleep etc. An example of an infinitive verb as a noun is: To swim a mile is her greatest dream. The infinitive form of the verb is "to swim"